Help diagnose problem with my amp

I have been using a Myryad SS integrated amp (MI-120, 60 watts/channel) in my system with ProAc D15's for a few years now. I have been plugging the amp into an Ensemble Isolink then to the wall. Last week, the volume has dropped by a quarter of the dial! I checked all connections etc. and nothing appears amiss. It's not just one speaker, both speakers now play at a far softer volume at 9 o'clock on the dial, which previously was plenty loud and detailed. I now have to turn the volume up to 12 o'clock for acceptable listening levels of depth, body and detail. This morning I wondered if somehow the Isolink had begun muting the amp's current, so I unplugged the amp from it and ran the power cord straight to the wall but no change. Any ideas?
With a tube amp I would assume a tube had blown with ss losing a transistor or resistor network is less likely but possible, how old is it, is it kept on continuously, can you get a measurement on the output voltage to check this?
Just some random thoughts
Did you change your speakers?
No I didn't change my speakers! Yes I wondered if a resistor or transistor had blown, but one that affects both channels. The amp is 10-15 yrs old I think, not sure, bought used.
Your amp came out in 1996 so it is max 15 years old. Call the company and see how old it is by serial number, that will give you a date for age. Tell them what has happened and they should be able to tell you in the ball park.
Depending on where it blew, if something blew, yes it could affect both channels, especially if it happened in the preamp section. Do you have another amp or preamp to stick in the circuit? How long have you had it? Something is not getting the gain it needs but if turned up high enough the signal comes through to the level you want.
It's possible there's an issue with the power supply voltages. Voltage regulators can fail and/or no longer regulate properly. Voltage may have dropped causing a decrease in gain. Depending on the circuit, that would account for both channels being down in level as they share a common voltage regulator. It's also possible a fuse or resistor in one of the power supply rails has failed. This can also cause a problem with the power supply voltage. If this is a tube unit, a tube that's common to both channels may have failed, usually the input tube.
Again, thanks for the suggestions. This is a SS not tube unit. I have contacted Myryad tech support in UK and hope to hear something from them. I really love this amp so hope I can get it repaired. I have no local stereo repair place and am not sure where I could send it in US.
I might be able to help....I'm in CA. Let me know.